The present invention is directed to a method and apparatus for epoxidizing an unsaturated oil or an alkyl fatty acid ester, particularly an unsaturated vegetable oil, such as soybean oil, linseed oil, or an ester of tall oil fatty acids. More particularly, the invention is directed to a thin-film method of epoxidizing an oil or an alkyl fatty acid ester by combining the oil or alkyl fatty acid ester with a combination of acetic or formic acid, hydrogen peroxide and with or without an acid catalyst selected from a strong mineral acid, such as H2SO4 or phosphoric acid, or styrene sulfonic acid, to produce peracetic or performic acid, in-situ, for reaction (epoxidation) with the oil or alkyl fatty acid ester, in a thin-film reactor.
Epoxy plasticizers, such as epoxidized unsaturated oils and, epoxidized alkyl fatty acid esters, particularly epoxidized soybean oil and epoxidized octyl esters of tall oil fatty acids can be manufactured by oxidation of either olefinic or aromatic double bonds, as follows: 
Hydrogen peroxide and the unsaturated oil or the alkyl fatty acid ester alone do not react to any significant extent, and an organic peracid (usually acetic acid or formic acid) is necessary to shuttle the active oxygen from the aqueous phase to the oil phase. Once in the oil phase, the peracid adds oxygen across the carbon-to-carbon double bond and regenerates the original acid. On a commercial scale, epoxidation of soybean oil is achieved by oxidation of soybean oil with peracetic acid 
where the peracetic acid is derived from the oxidation of acetic acid with hydrogen peroxide, in-situ, in the presence of the soybean oil. In one process, peracetic acid generated in a process for oxidation of acetaldehyde to acetic acid has been isolated and used in the epoxidation process. This preformed peracetic acid can be handled, with proper precautions, in an inert solvent such as ethyl acetate or acetone. Others have found that an intermediate in the acetaldehyde oxidation process, acetaldehyde monoperacetate, also can be used as an epoxidizing agent. While oxidation of olefins by hydroperoxides is described in the literature, these prior art processes are far less efficient than the peracid processes.
The epoxidation processes can be divided into two basic types. In the first, the peracid is preformed; in the second, the peracid is formed in-situ, that is in the primary reaction vessel. Representative schematics for the preformed and in-situ processes are shown in FIGS. 1A and 1B. The processes claimed herein are directed to a new and improved in-situ process.
Preformed Peracetic Epoxidation
The use of preformed peracetic acid results in epoxidation without catalyst at temperatures of 20 to 60xc2x0 C. at atmospheric pressure, as follow: 
The peroxidation of acetic acid with hydrogen peroxide is not efficient except at high molar ratios of acetic acid to hydrogen peroxide, resulting in large amounts of acetic acid to be recovered. In addition, concentrations of peracetic acid above 40 to 45 wt. % in acetic acid are explosive at epoxidation temperatures. Such processes require large volume production on an essentially continuous basis since the preformed peracid cannot be safely stored.
In-Situ Epoxidationxe2x80x94Acid Catalyzed
Experience has shown that the in-situ process is safer than processes using preformed peracids. In general, a peroxide solution (35% to 70% H2O2 in water) containing small quantities of a strong mineral acid catalyst, such as sulfuric acid or phosphoric acid, or styrene sulfonic acids, is added to a mixture of an epoxidizable substrate and acetic acid or formic acid at atmospheric pressure. As the reactants mix, the hydrogen peroxide and the acetic or formic acid react in the presence of the mineral acid catalyst to form the peracid, as follows: 
To prevent uncontrolled exotherm and to optimize epoxidation, the peroxide solution is added in several increments with agitation, and the reaction temperature is maintained at 50xc2x0 C. to 65xc2x0 C. for periods of 10 to 40 minutes per incremental addition of peroxide. One of the biggest problems with this process is that only small batch quantities of peracid can be formed in the presence of the unsaturated substrate. The peracid reacts with the unsaturated portion of the molecule and is quickly depleted, preventing a build-up of detonatable quantities of peroxide compounds, as follows: 
Further, significant problems are encountered in separation of the epoxidized substrate from the water, acid and peroxide remaining with the product after reaction. When the iodine number of the substrate has been reduced to the desired level, e.g, 0.5 to 10, the reaction is stopped and the epoxidized substrate is then difficult to separate from the aqueous layer since the aqueous layer contains a mixture of water, organic acid and some peroxide. Further, the epoxy layer contains acid-catalyst that must be neutralized by a mild base, and residual peroxide that must be decomposed. The epoxy then is washed and transferred to a stripper where water and non-product residues are removed.
Most, if not all of the above-identified difficulties of the known in-situ epoxidation processes are eliminated, or substantially reduced in accordance with the processes described herein.
The processes described herein take advantage of thin-film reactor apparatus for epoxidizing an unsaturated oil, such as soybean oil, linseed oil, or an alkyl ester of a fatty acid (hereinafter, the epoxidized unsaturated oil and/or the epoxidized alkyl fatty acid ester are referred to as the xe2x80x9cepoxidized substratexe2x80x9d). In accordance with the processes described herein, the unsaturated substrate is reacted with a preformed peracid (FIG. 2B), e.g., peracetic acid or performic acid, in a thin-film reactor, or the peracid can be formed, in-situ, within the thin-film reactor, as shown in FIG. 2A, by reaction with an organic acid, such as acetic acid and/or formic acid, capable of being oxidized to a peracid, with or without an acid catalyst, such as a strong mineral acid, such as sulfuric or phosphoric, or styrene sulfonic acid, to accomplish oxidation of the organic acid to a peracid. In accordance with the preformed peracid embodiment, the peracid can be preformed in an ion-exchange bed and then fed to the thin-film reactor for reaction with the unsaturated substrate by ion-exchanging a mixture of and oxidizing agent, e.g., hydrogen peroxide, and an organic acid, particularly acetic acid or formic acid, with an ion-exchange resin, particularly an acid ion-exchange resin, such as a styrene sulfonic acid resin, e.g., AMBERLYST, or a methane sulfonic acid resin, e.g., AMBERLITE of Rohm and Haas, or a styrene divinyl benzene resin, e.g., DOWEX NCR of Dow Chemical. Both thin-film processes can be operated continuously while continuously stripping most of the water, acetic or formic acid, or peracid, and optional acid catalyst from the epoxidized product in the thin-film reactor. The thin-film reactor processes described herein can strip sufficient water, acid catalyst (if used) from the reaction product (epoxidized substrate) so that the epoxidized substrate requires little or no additional purification and the excess acetic or formic acid and the acid catalyst (if used) can be recycled to the continuous process.
Accordingly, one aspect of the processes described herein is the rapid removal of water, in the vapor phase, to allow increased rates of reaction (epoxidation) of unsaturated compounds.
Another aspect of the processes described herein is the elimination or substantial reduction of the neutralization, washing, decanting, and/or filtration steps needed with the presently practiced epoxidation processes.